Presently, there are a number of randomly dumped and self orientable packing elements of other than spiral form such as disclosed in U.S. Pat. Nos. 2,055,162; 2,376,349; 3,914,351; 3,957,931 and 4,067,936. Others of spirally wound corrugated ribbon form, which are stacked and not dumpable, are disclosed in U.S. Pat. Nos. 2,940,168 and British Pat. No. 937,597.
Some of the prior art elements have a maximum transverse dimension or diameter greater than the axial height or length between the opposite sides or ends thereof. Hence, they have a tendency when stacked to remain in that position and when randomly dumped to assume a position, with its maximum transverse dimension and opposite sides thereof extending substantially horizontal.
Also, disclosed in said British Patent are continuous ribbons of suitable thermoplastic material which can be spirally wound to form elements of other geometrical shape such as rectangular or square.
When packing elements with long vertical dimensions are stacked in a bed there is substantially no cross flow of liquid normal to the direction of gas and liquid flow. As a result the initial pattern of liquid distribution imposed above the bed, continues substantially uninterrupted through the bed. Thus any dry areas at the top of the bed continue to be dry throughout the bed with the resultant loss of volume of the packing actually engaged in mass transfer.
The dumpable spiral packing elements of the invention disclosed hereinbelow have superior performance with respect to orienting themselves horizontally, resistance to fouling and the ability to slough solids and biomass. This is because substantially all of the surface area will orient in a substatically vertical mode, and the shorter vertical surfaces of adjacent non-aligned elements will more frequently interrupt the liquid or effluent flow. Interruptions of flow of course, enhances oxygen absorption or mass transfer. Further, because the spiral packing elements do not have a uniform radius, they have a greater tendency when dumped to orient in a random fashion with respect to any cross section of the tower normal to the direction of gas and liquid flow. This avoids pattern packing of the elements within the bed and contributes to improved internal liquid distribution. Also, because the packing media or elements are placed at random and are not stacked members with long vertical dimensions, apparatus packed with the spiral elements of the invention is much less sensative to the quality and non-uniformity of the initial liquid distribution above the bed.